1. Technical Field
The present invention relates to image-capturing apparatuses that use linear image sensors to perform high-speed, high-quality capture of image information, and that have a still-original data-capture mode for capturing information from documents placed on a platen, and a moving-original data-capture mode for capturing information from documents conveyed from a document conveyance device.
2. Description of the Related Art
Image-capturing apparatuses installed in copiers, facsimile machines, etc. are of late increasingly being expected to manage both accelerated document-scanning speed and heightened image quality. Document image-data capture at high image quality and with exactitude is possible in practice by slowing the relative speed between the document and the data-capturing means that scans images on the document. On the other hand, if the relative speed is quickened, the level of electric charge output from the image sensors will drop, because the sensors' charge-storing time is shortened, inviting compromised image quality. Thus, the heightened speed and heightened image quality expected of image-capturing apparatuses are conflicting demands.
Against this backdrop, as a method to manage both heightened speed and heightened image quality in image data capture, apart from speeding up the data read-out rate at which data is read-out data from CCDs, document scanning by a plurality of scanning lines simultaneously is carried out. (Cf., for example, Japanese Unexamined Pat. App. Pub. No. H11-55474.)
The image-capturing apparatus set forth in JP H11-55474 is equipped with a linear sensor exemplarily furnished with two photoreceptors—a first photoreceptor and a second photoreceptor—in a row for capturing image data from documents, and therein is designed to realize high-quality image data acquisition and high-speed image data capture by delaying output from the first photoreceptor using a delay circuit, and by adding the delayed output from the first photoreceptor to output from the second photoreceptor.
Thus, the fact that the image-capturing apparatus set forth in JP H11-55474 is configured in such a way that of the two—the first and second—photoreceptors, one—the first photoreceptor—is furnished with a delay circuit means that either the image-capturing unit or the document original must necessarily be shifted in the direction in which the first photoreceptor captures original-document image data, ahead of the second photoreceptor. Put differently, the linear sensor has directionality.
Image-capturing apparatuses having an automatic document feeder (hereinafter termed “ADF” for convenience), however, ordinarily have two document-data capture modes—not just a still-document data-capture mode for capturing data from a document original placed on the platen, but also a moving-original data-capture mode as well, for capturing data from conveyed document originals. In an implementation in which the directions in which documents are scanned in these two modes are reversed, adopting the directionalized linear sensor set forth in JP H11-55474 would mean that the delay circuit could be used in only one of either of the data-capture modes.
Specifically, an implementation in which a delay circuit can be used in the moving-original data-capture mode will create a situation in which the circuit cannot be used in the still-original data-capture mode; conversely, an implementation in which a delay circuit can be used in the still-original data-capture mode will create a situation in which the circuit cannot be used in the moving-original data-capture mode. Consequently, to date it has not been possible to perform scanning at high speed and with high-image quality in both data-capture modes—the still-original data-capture mode and the moving-original data-capture mode.